Reducing the thermal conductivity of La2Mo2O9 with a trivalent praseodymium substitution for its potential use as a thermal barrier coating

Abstract

(La_1−xPr_x)₂Mo₂O₉ powders were synthesized by solid state reaction for x = 0.00, 0.10, 0.25, 0.50, 0.75 and 1.00. Dense pellets were obtained by conventional sintering in air. Their thermal stability and thermal conductivity were measured from 100 to 700 °C and their cell parameters refined from X-ray powder diffraction pattern by the Rietveld method. A 50 mol% isovalent substitution of lanthanum in La₂Mo₂O₉ by praseodymium stabilizes the high temperature β phase while reducing the thermal conductivity of the parent compound by 11–18%. For a praseodymium content x higher than 0.75, the thermal conductivity increases and a phase transition similar to that of La₂Mo₂O₉ is observed except that the room temperature phase appears to be this time triclinic in symmetry.